A typical hollow fiber filter device is an apparatus having a plurality of fine, hollow, permeable (or semi-permeable) fibers, the ends of which may be embedded or potted in a plastic resin header or sealing compound. After the resin cures, a portion of the header is cut, usually transverse to the longitudinal axis of the fibers, so that the ends of the fibers are exposed, thus allowing communication with the interior of the fibers. The hollow fiber devices are typically fabricated as units, referred to herein as modules, usually by casting the fibers in a U or hair-pin shape.
Hollow fiber filter devices typically filter a liquid or gas by passing the filtrate through the module and/or over the hollow fibers. In outside to inside fluid flow filtration, the filtrate passes from the outside of the fiber to the inside, leaving the undesirable component on the outside. The filtered component, on the inside of the fiber, then passes along the inside until it is discharged from the end of the module. In dead-end separation devices, the undesirable component may form a filter cake or filter layer along the outside of the fibers.
A wide variety of publications exist pertaining to the preparation and use of these devices. For example, hollow fiber filter devices have been used in gas-gas, gas-liquid, liquid-liquid, liquid-solid, etc. separations, primarily in water desalination, dialysis, microfiltration to remove bacteria and other fine particles from a liquid, detoxification of industrial wastes/sewage treatment, and ultrafiltration to remove very fine or dissolved solids from a liquid. The modules of the present invention are particularly suited for environments in which the liquid to be filtered is already relatively clean or pure, e.g., for use in the production of ultra-pure water used in electronics manufacturing.
Problems associated with the production of these devices are also well known, e.g., pressure build-up in the potted fibers; production of a clean, open fiber opening; formation of an adequate bond between the potting material and the fibers; and the expense in both time and money in using thermoset or epoxy-type potting resins. Furthermore, hollow fiber filter devices have typically not been capable of production using injection molding techniques, due to the fragility of the fibers and the high temperature conditions used in injection molding. For example, while the hollow fibers may be produced from a thermoplastic polymer, such fibers are not always adequately sealed by the potting compound and may flow or deform under elevated temperatures. Potting methods have been developed, therefore, which require a multiple-part system such as an epoxy and a urethane; however, these multiple-part systems are typically very time consuming and expensive, and do not consistently result in a adequate bond between the outer surface of the hollow fibers and the potting material. In addition, in the typical process employed by the prior art, the ends of a plurality of hollow fibers are bundled and placed in a mold which is then filled with a potting resin. The bundle must be fixed in the filled mold until the thermosetting potting compound cures.